Photoshop
Yes, you need to do it as a batch process. To do this you need to record a macro (known in photoshop as "Actions").
First, take any subject image you don't much care about. Then, in the actions pallete (Choose WINDOW > Actions), click the NEW button. Give it a name, such as "Resize images". Leave all other setting as default and click RECORD. Then, perform the task you want to do to all images. So you would want to go IMAGE > Image Size... and choose another size. I would reccomend you do it as a percentage because arbitrary values could skew images of different aspect ratios. Click OK. If that is all you would like to do, click STOP in the Actions pallete. Now you can close this temporary subject image, just choose NO to save changes. Now, click FILE > Automate > Batch processes. Under "Action", choose your action, called "resize images" or whatever you named it as. Make sure all the images you want to do this to are in one folder, and choose "Origin: Folder". Then choose whether you would like to simply overwrite the images, called "Save and close" (NOT reccomended) or save them to another folder (Much better idea so you still have the originals). Choose your naming preferences, and finally click OK. With any luck, all your images should be resized.
First, take any subject image you don't much care about. Then, in the actions pallete (Choose WINDOW > Actions), click the NEW button. Give it a name, such as "Resize images". Leave all other setting as default and click RECORD. Then, perform the task you want to do to all images. So you would want to go IMAGE > Image Size... and choose another size. I would reccomend you do it as a percentage because arbitrary values could skew images of different aspect ratios. Click OK. If that is all you would like to do, click STOP in the Actions pallete. Now you can close this temporary subject image, just choose NO to save changes. Now, click FILE > Automate > Batch processes. Under "Action", choose your action, called "resize images" or whatever you named it as. Make sure all the images you want to do this to are in one folder, and choose "Origin: Folder". Then choose whether you would like to simply overwrite the images, called "Save and close" (NOT reccomended) or save them to another folder (Much better idea so you still have the originals). Choose your naming preferences, and finally click OK. With any luck, all your images should be resized.
Well I have to resize photos frequently and have set up a Photoshop Action for it, which is just like a Macro.
Basically because all the original pictures are the same size and the target size is always the same, all I did was when I did the first picture I started 'recording' an action and now all I have to do is play that action for each picture I want resizing - I still have to open every picture and set the action playing but it's a lot quicker than resizing each photo individually.
This may not be the best way of doing it but it's the best I could find, and of course it only really works when all the original pictures are the same size and all the edited pictures are the same size.
I don't know if that's any help but thats the way I do it
Edit: CDD beat me to it with a better explanation and a better way for me to do it! Thanks! 
Basically because all the original pictures are the same size and the target size is always the same, all I did was when I did the first picture I started 'recording' an action and now all I have to do is play that action for each picture I want resizing - I still have to open every picture and set the action playing but it's a lot quicker than resizing each photo individually.
This may not be the best way of doing it but it's the best I could find, and of course it only really works when all the original pictures are the same size and all the edited pictures are the same size.
I don't know if that's any help but thats the way I do it
Edit: CDD beat me to it with a better explanation and a better way for me to do it! Thanks!
Dan